The present invention relates to image sensors in general, and in particular to new designs of pixel, column circuitry, and matrix controller, that enable image sensors to operate in a photo-current mode. The photo-current mode can be used for imaging purposes to expand the intra-scene dynamic range, and also to enable the entire sensor matrix to operate as a “pixelated” solar cell.
With the exception of the 3T Logarithmic pixel, which is not the most widely used CMOS pixel design, none of the other conventional CMOS Image Sensors (CIS), are capable of operating in a photo-current mode for image sensing purposes.
None of the conventional image sensors, CCDs and/or CIS, make use of the photo-diode in each pixel cell to generate electrical power, when not in use for image sensing. The readout of CCDs proceeds by applying voltage pulses to each pixel, in a particular sequence, in order to shift, sequentially for each pixel, the accumulated charges to the edge of the pixel matrix, and outside the CCD integrated circuit. This type of operation is not suitable to use the accumulated charges to generate electrical power.
The readout of CIS Active Pixel Sensors (APS), regardless if the pixel is a 3T, 4T, 3T Logarithm, etc, is done through the transconductance amplification of a MOSFET inside the pixel, which by definition would not allow photo-current to flow into the column bus.
These basic architectural features of CCDs and CIS APS technologies, do not allow the current collected in the photo-diode of each pixel, to be used for electrical power generation.
The present invention allows many different types of image sensors to use the photo-diode in each pixel for the purpose of generating electrical power, when not in use for image sensing.
The present invention is also applicable to the photo-diode and pixel cell technology described in U.S. Pat. Nos. 6,943,051; 7,153,720; 7265,006, U.S. patent application Ser. No. 11/781,544; WO 2004/027879.